This invention relates to a work moving device for a sewing machine.
Conventionally, an electronic cycle sewing machine has a work moving device which moves a work-to-be-sewed (or workpiece) with respect to the sewing needle according to the given sewing data in a pattern stitching operation. A variety of work moving devices of this type have been proposed in the art. Work moving devices which have been disclosed, for instance, by Unexamined Japanese Patent Publication No. Sho. 58-500744 and Examined Japanese Patent Publication No. Hei. 1-45395 are well known in the art.
The device disclosed by Unexamined Japanese Patent Publication Sho. 58-500744 has a frame which moves on a pair of guides at a predetermined height. The frame has a movement axis which is extended laterally with respect to the direction of movement of the frame. A carriage is provided in such a manner that it is movable along the movement axis. The carriage is used to position a work with respect to the sewing needle which is moved back and forth, including for instance a holder adapted to support the work. More specifically, the carriage is provided with a pair of gear racks which are coupled to the frame and extend in the direction of movement of the frame and a drive mechanism for driving the gear racks so that two drive forces are applied to the frame through the gear racks.
The device disclosed by Examined Japanese Patent Publication No. Hei. 1-45395 comprises: a pallet which positions a work in place with respect to a sewing machine body having seam forming means; a carriage on which the pallet is detachably supported; a movable frame on which the carriage is supported in such a manner that it is moved back and forth in one direction; a pair of stationary racks with guide members which are provided below both ends of the movable frame in such a manner that they extend in a direction perpendicular to the direction of movement of the carriage; a shaft having a pair of gears at both ends which are engaged with the stationary racks, the shaft being rotatably supported on the movable frame; a sliding body which is provided on the movable frame, the sliding body being guided on the aforementioned guide members so that the movable frame is moved along the guide members; a drive rack which is fixedly provided substantially at the middle of the movable frame in such a manner that it is extended in parallel with the stationary racks; a first electric motor which engages with the drive rack to drive the latter together with the movable frame; and a second electric motor which is so arranged as to drive the aforementioned carriage in a direction perpendicular to the direction of movement of the movable frame.
The above-described work moving devices have several problems. In the former device (disclosed by Unexamined Japanese Patent Publication No. Sho. 58-500744), the drive mechanism for moving a workpiece is so designed as to provide two drive forces; that is, it has two electric motors for moving the work in one direction. Hence, the device is high in manufacturing cost. In addition, it is difficult to make the operations of the motors synchronous with each other.
The latter device (disclosed by Examined Japanese Patent Publication No. Hei. 1-45395) is free from the above-described difficulties, because the drive mechanism has only one electric motor. However, the moving drive rack is heavy. Therefore, the device is not suitable for moving a work at high speed. In addition, two stationary racks and one drive rack are arranged in parallel with one another. During installation it is rather difficult to arrange them in parallel with one another with high accuracy. Furthermore, the drive rack and its guide, being arranged substantially at the middle of the movable frame, may obstruct the replacement of the bobbin in the shuttle of the sewing machine.